ActivityBot: board no longer works with servos connected

The robot worked fine until yesterday, when any attempt to load new programs (either to RAM or EEPROM) started failing with "no propeller chip on port". I disconnected all devices, one at a time, and found out that the servo connections are the deal breakers. Once disconnected, the board is working again.

Any advice?

Thanks,
--Elad

Comments

  • 13 Comments sorted by Date Added Votes
  • ercoerco Posts: 18,496
    New batteries.
    "When you make a thing, a thing that is new, it is so complicated making it that it is bound to be ugly. But those that make it after you, they don’t have to worry about making it. And they can make it pretty, and so everybody can like it when others make it after you."

    - Pablo Picasso
  • I actually thought of that, but couldn't possibly see how that could be related to the symptom.
    I'll give it a try.

    Thanks!
  • Duane DegnDuane Degn Posts: 10,002
    edited April 10 Vote Up0Vote Down
    Servos suck a lot of power. When the batteries get low they can't source enough current for the servos and the voltage of the pack ends up dropping too low for the microcontroller to work properly.

    It is very common for people new to robotics (including myself a few years ago) to underestimate the amount of power required by servos.
  • I am by no means underestimating the energy requirements of the servos, but something still seems wrong here. I disconnected the battery pack from the board, set the three-way switch to position 1 and still see the problem as long as the servo cables are connected to the board. A potentially-related problem is that even when the three-way switch in is position 1, both the #1 and #2 green LEDs are on. I am pretty that it used to be that only LED 1 would turn on when the switch was in position 1.
  • Do you know how old this Activity board is? I think some of the earlier boards had bad switches.
  • I'll add, I've had trouble with an Activity board when I powered the board from a battery while also connecting to USB.

    I suggest unplugging a battery whenever you program the board. I don't know if the newer boards have this problem but I burned out an older board this way.
  • Thanks Duane. I don't know how old the board is, but it came in as part of an ActivityBot purchase in December. For the record, it is the WX variant, which I believe is fairly new.

    The tests I ran were with the battery pack disconnected.
  • I'm asking our Tech Support staff to visit this thread.
  • Hi Elad,

    When you get 2 green power leds turning ON when you have the switch set to position 1 is a common symptom to a shorted board. One of the logic transistors is blown. The board can still potentially work, however you won't be able to turn off the servo headers. They will always remain ON.

    There had to of been a short on the board if it was not working until you disconnected the servos. Either the servos themselves were connected wrong or another circuit you built may have been causing it.

    Also if it seems like the servos are sluggish check that the jumper next to servo port P12 is jumped to Vin and not 5V.

    Miguel Rodriguez
    Parallax Tech Support


  • ercoerco Posts: 18,496
    BTW, welcome to the forums, Elad. Hopefully Miguel's comment helps you sort out your issue.

    Looks like you joined a few months ago and I'm sure you've noticed that this is a very friendly and helpful place. How great is it that Ken (the President of Parallax) personally responded to your post and got Tech support involved?

    Keep us updated on your progress, Team Parallax is here to assist.
    "When you make a thing, a thing that is new, it is so complicated making it that it is bound to be ugly. But those that make it after you, they don’t have to worry about making it. And they can make it pretty, and so everybody can like it when others make it after you."

    - Pablo Picasso
  • Thanks, Miguel. The interesting part is that everything worked well (including the servos and the various circuits my son and I built) up until this weekend.
    Is the situation hopeless, then?

    erco, I will do my best to keep the forums friendly and helpful ;-)
  • From what you describe it sounds like the board is still functional the only thing is that the servo headers will have to always be ON. Its not necessarily a show stopper. Whenever you load a program that involves moving the servos prop the AB up so that the wheel do not touch the ground. This will keep it from taking off when you load a program that involves motion.
  • Hi Elad,

    Having an issue with my account however the last comment coming from ELEV-8 Flight Crew is actually from me.
    Please let me know if you have more questions.

    Miguel Rodriguez
    Parallax Tech Support
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